Syncope - Faint - Blackout

Epidemiology

The cumulative lifetime prevalence is about 15% of the population. It is commoner in females.

Pathophysiology

Syncope results from transient reduction of cerebral blood flow with consequent cerebral hypoxia. The commonest cause is vasovagal syncope, in which reflex loss of arterial tone is followed by hypotension and bradycardia; pain, fear, coughing and micturition are common precipitating factors. Other causes of syncope include: orthostatic hypotension (eg pregnancy), carotid sinus hypersensitivity, drugs, autonomic failure, cardiac failure, cardiac arrhythmia.

Clinical Features

A detailed history from the patient is the diagnostic keystone. The context of the event is a very important clue. "The nurse had just finished taking some blood". "It was the first time I had been to the operating theatre". Syncope typically occurs on standing, but may happen when sitting: a syncopal type attack on lying down should raise suspicion of a serious cardiac cause.

There is a prodrome of feeling unwell, perhaps with nausea and sweating. There is a sense of impending loss of consciouness, which may be described as dizziness, a swimming feeling or lightheadedness. The vision goes dark and sounds become fainter. This is followed by loss of consciousness, although the patient will often say they can still hear things around them. They fall to the ground; eye-witness descriptions often mention the person sliding, crumpling or folding down to the floor (reflecting the hypotonia). The patient will look pale and limp. There are frequently intermittent jerky movements of the limbs and sometimes transient hypertonia. The patient is usually alert on recovering consciousness, although may feel frightened and unwell. Serious injury is rare in vasovagal syncope in young people, but falls in the elderly are a common cause of fracture. An anoxic seizure can occur if the patient is maintained in an upright position.

Neurological examination is normal. Clinical evidence of postural hypotension or cardiac disorder should be sought.

Investigation

A typical attack of vasovagal syncope, with a normal clinical examination, in a child or young adult needs no further investigation.

Frequent attacks or attacks in the elderly require investigation to look for underlying cardiac and circulatory causes. The precise investigations will vary according to the individual circumstances but may include: appropriate haematology and biochemical screen, ECG, CXR, 24 hour ECG, cardiac memo, tilt-table test.

Management

An explanation and reassurance is required for simple vasovagal syncope. Cardiac arrhythmias and other circulatory disorders may be managed with medication, pacing or surgery and require referral to a cardiologist.

Prognosis

Syncope in young people is usually self limiting. It may be associated with disability in the elderly due to secondary complications e.g. fracture.

References and Links

Fitzpatrick A, Sutton R. Tilting towards a diagnosis in recurrent unexplained syncope. Lancet 1989; 1(8639): 658-60.

Petch MC. Syncope. An accurate history tells all. BMJ 1994; 308: 1251-2.

Linzer M et al. Diagnosing syncope. Part 2. unexplained syncope. Clinical efficacy assessment project of the American College of Physicians. Ann Intern Med 1997; 127: 76-86.